1. Field of the Invention
The present invention relates to an actuator unit which is mounted on a lens driving device and utilizes an electromagnetic driving mechanism to enable a lens support supported by a spring component in a suspended manner to move.
2. Description of Related Art
FIG. 14A and FIG. 14B are diagrams illustrating an example of an existing voice coil motor type lens driving device 30.
As shown in FIG. 14A, the lens driving device 30 is formed to be box-shaped and is composed of an actuator unit 40, a magnet yoke 32 for storing the unit, and a base 39. The actuator unit 40 arranged on the inner side of the magnet yoke 32 is utilized to enable a lens 31 to move towards the front of Z axis (+Z axis direction) or the back of Z axis (−Z axis direction) as the optical axis, and enable an image of an object positioned in front of the lens 31 to be focused on an image sensor assembled at the back of the lens. As shown in Patent Document 1, JP patent No. 2004-280031 literature, the representative structure of the same lens driving device intimately has been well known.
The actuator unit 40 as shown in FIG. 14B utilizes a lens support 37, an electromagnetic driving mechanism 42 and a spring component 34 to enable the lens 31 to move to a preset position. The spring component 34 is composed of a front side spring component 34A and a back side spring component 34B which are in an approximately same structure. Moreover, the electromagnetic driving mechanism 42 is composed of a coil 38 for driving the lens mounted on the lens support 37 arranged on the moving side and a magnet 35 for driving the lens arranged on the fixed side.
The lens support 37 as shown in FIG. 14B and FIG. 15 is open along the Z axis direction to form a cylinder shape with a circular opening part 37c, and the lens 31 is retained by the inner circumference side of the opening part 37c. 
The coil 38 as one component of the electromagnetic driving mechanism 42 is cylindrically wound on the periphery of the lens support 37 around an axis parallel to the Z axis. The magnet 35 as another component of the electromagnetic driving mechanism 42 is formed to be trapezoid column-shaped and is disposed on the outer side of the coil 38 around the axis parallel to the Z axis at a 90-degree interval. The outer circumference side face of the coil 38 and the magnetic pole face of the magnet 35 are disposed opposite to each other at an interval in the radial direction.
A front side magnet support 36A is provided with side walls 36c protruding towards the back of Z axis at central parts of the sides and forms into a square frame-shape with an opening in the Z axis direction. A back side magnet support 36B is provided with an opening in the Z axis direction and forms into a square frame-shape. The magnet 35 is clamped at corners of the square frame by the four sides and the side wall 36c of the front side magnet support 36A and the four sides of the back side magnet support 36B.
Inner side retaining parts 34a of the front side spring component 34A and the back side spring component 34B are respectively connected to a front side connecting end 37a arranged in front of the lens support 37 in the Z axis direction and a back side connecting end 37b arranged at the back of the lens support 37, and outer side retaining parts 34b of the front side spring component 34A and the back side spring component 34B are respectively connected to the front side end part 36a of the front side magnet support 36A and the back side end part 36b of the back side magnet support 36B. Therefore, the actuator unit 40 is formed.
When the coil 38 of the actuator unit 40 is electrified, the coil 38 generates Lorentz force in the +Z axis direction, and the lens support 37 is moved to a position balanced with restoring force of the spring component 34. Therefore, the lens 31 retained on the lens support 37 can move to the preset position in the Z axis direction.
As mentioned above, the actuator unit 40 is retained on the +Z side and the −Z side by the magnet yoke 32 and the base 39, and is assembled in the lens driving device 30.
The magnet yoke 32 is formed into a box shape by side faces 32a arranged in front of the actuator unit 40 and formed by four surfaces parallel to the Z axis and a top surface 32b prolonged from the +Z side end part of the side faces 32a to the inner radial direction and provided with an opening part 32c at the central part, and the magnet yoke 32 covers the front part and the side faces of the actuator unit 40. The magnet yoke 32 is used for improving the magnetic intensity generated onto the coil 38 from the magnet 35, and shielding electromagnetic waves emitted out from the coil 38 or the unshown image sensor.
The base 39 is arranged at the back of the actuator unit 40, and includes: a plate-shaped base plate 39b, a frame-shaped side wall 39c vertically arranged from the outer edge of the base plate 39b in the +Z axis direction, a deep digging part 39d formed by deep digging from the inner radial side of the base plate 39b to the back of the Z axis direction, a circular ring-shaped limiting part 39e which is protruding from the inner edge of the deep digging part 39d to the side of the lens support 37 and abuts against the back side end part 37e of the lens support 37 when the coil 38 is not electrified so as to limit the lens support 37 at the backmost position, and a circular opening part 39a which is formed in the inner edge of the limiting part 39e and faces to the Z axis direction.
As shown in FIG. 14B and FIG. 16A, the spring component 34 is integrally formed by the following components: a circular ring-shaped inner side retaining part 34a connected to the lens support 37; a square frame-shaped outer side retaining part 36b connected to the magnet 35; a plurality of wrist parts 34c disposed between the inner side retaining part 34a and the outer side retaining part 34b and provided with a bending part 34d at the central part; a plurality of inner side connecting parts 34e for connecting the inner side retaining part 34a with one ends of wrist part 34c; a plurality of outer side connecting parts 34f for connecting the outer side retaining part 34b with the other ends of the wrist parts 34c. 
When each wrist part 34c is observed from the +Z side, the writ part is prolonged anticlockwise (or anti-anticlockwise) along the peripheral direction from the inner side retaining part 34a through the inner side connecting part 34e, and is connected with the outer side retaining part 34b through the outer side connecting part 34f. These wrist parts 34c is taken as a spring for suspending the lens support 37 in the actuator unit 40 to take effect.
In the lens driving device 30, a square frame-shaped fixed ring 33 (reference to FIG. 15) is inserted into the inner side of the magnet yoke 32 from the −Z side. Moreover, the actuator unit 40 is inserted in the −Z side of the fixed ring 33, and the outer side retaining part 34b is clamped by the top surface 32b of the magnet yoke 32 and the front side end part 36a of the front side magnet support 36A with the help of the fixed ring 33. The actuator unit 40 is inserted in the inner side of the side wall 39c of the base 39 pressed from the −Z side, and the outer side retaining part 34b of the back side spring component 34B is clamped by the base plate 39b of the base 39 and the back side end part 36b of the back side magnet support 36B.
Finally, the lens is mounted in the lens support 37, and the lens driving device 30 is assembled. The unshown image sensor assembled on the −Z side of the assembled lens driving device 30 is taken as an auto focus camera, and is assembled in a cellular phone for instance.
However, the spring component 34 is formed by thin and narrow panel, and thus the wrist parts 34c are likely to be deformed in the Z axis direction taken as the running direction, and are likely to be subjected to micro external force as shown in FIG. 16B so as to be deformed in the directions orthogonal to the Z axis (X axis direction, Y axis direction).
Before the spring component 34 as shown in FIG. 16A is assembled, the spring component 34 is not subjected to external force, the outer side retaining part 34b and the inner side retaining part 34a of which cannot exist a position offset, so the center P1 of the outer side retaining part 34b and the center P2 of the inner side retaining part 34a can keep consistent with each other. However, as shown in FIG. 16B, for example, when the inner side retaining part 34a is just subjected to micro force in the direction orthogonal to the Z axis, the wrist parts 34c are likely to be distorted (deformed) in the direction orthogonal to the Z axis, and the center P2 of the inner side retaining part 34a and the center P1 of the outer side retaining part 34b may exist an offset. In the working procedure that the spring component 34 is connected, the wrist parts 34c are likely to be distorted in the direction (X axis direction, Y axis direction) orthogonal to the Z axis, which results in that the assembled lens driving device 30 is inclined during running.
Namely, in the lens driving device 30, wrist parts 34c of the front side spring component 34A or the back side spring component 34B are assembled in the actuator unit 40 at the state of being distorted in the direction orthogonal to the Z axis. When the coil 38 is electrified so as to enable the lens support 37 to begin to move forwards in the Z axis direction, the lens support 37 may be twisted around the axis forming a right angle with the Z axis, and the optical axis of the lens 31 is inclined.
Hereon, refer to the FIGS. 17A, 17B, 17C and 17D, the assembling working procedure and inclination of the actuator unit 40 are described in detail. During the assembling of the actuator unit 40, a back side spring component mounting clamp 41B, a front side spring component mounting clamp 41A and a centering clamp 41C are used.
The back side spring component mounting clamp 41B is plate-shaped, and the central part of which is provided with an opening part 41c for the centering clamp 41C to detachably buckle. And for the sake of positioning, the back side spring component mounting clamp 41B includes: a first deep digging part 41d and a second deep digging part 41e. The first deep digging part 41d is processed to be corresponding to the shape and the size of the front side magnet support 36A so that the front side magnet support 36A can be inserted in the first deep digging part 41d. The second deep digging part 41e is processed to be corresponding to the shape and the size of the lens support 37 and is processed with an appropriate depth.
The front side spring component mounting clamp 41A is plate-shaped, and the central part of which is provided with an opening part 41a for the centering clamp 41C to detachably buckle, and the front side spring component mounting clamp 41A is also provided with a third deep digging part 41b for positioning, which is processed to be corresponding to the shape and the size of the back side magnet support 36B so that the back side magnet support 36B can be inserted in the third deep digging part 41b. The centering clamp 41C is column-shaped, and is processed to be corresponding to the shape and the size of the inner wall 37d of the lens support 37 and the inner wall 37d of the lens support 37d can be inserted in the centering clamp 41C.
The assembling working procedure of the actuator unit 40 includes: the working procedure for connecting the back side spring component 34B onto the lens support 37 and the back side magnet support 36B; and the working procedure for respectively connecting the front side spring component 34A onto the lens support 37 and the front side magnet support 36A.
Namely, as shown in FIG. 17A, the first deep digging part 41d and the second deep digging part 41e are respectively aligned to the opening part 41c of the back side spring component mounting clamp 41B facing to the −Z side and the +Z side end part of the centering clamp 41C mutually. Moreover, the centering clamp 41C is inserted into the inner wall 37d of the lens support 37 wound with the coil 38 from the −Z side end part, the front side end part of the lens support 37 abuts against the second deep digging part 41e of the back side spring component mounting clamp 41B, and the front side magnet support 36A abuts against the first deep digging part 41d of the back side spring component mounting clamp 41B. In this way, the centering clamp 41C is utilized for the positioning of the lens support 37 in the diameter direction, and the second deep digging part 41e of the back side spring component mounting clamp 41B is utilized for the positioning of the lens support 37 in the Z axis direction, and the first deep digging part 41d is utilized for the positioning of the front side magnet support 36A in the diameter direction and the Z axis direction.
And then, after the magnet 35 and the back side magnet support 36B are overlapped in sequence on the −Z side of the front side magnet support 36A so as to be connected with each other, the inner side retaining part 34a of the back side spring component 34B is connected to the back side connecting end 37b of the lens support 37, and the outer side retaining part 34b is connected to the back side end part 36b of the back side magnet support 36B.
Then, as shown in FIG. 17B, in the state that the back side spring component 34B, the lens support 37, the front side magnet support 36A, the magnet 35 and the back side magnet support 36B are connected mutually and mounted on the centering clamp 41C, the back side spring component mounting clamp 41B is demounted from the centering clamp 41C. Moreover, the third deep digging part 41b is respectively embedded with the opening part 41a of the front side spring component mounting clamp 41A facing to the +Z side and the −Z side end part of the centering clamp 41C, and the back side magnet support 36B abuts against the third deep digging part 41b of the front side spring component mounting clamp 41A. Thereafter, the front side spring component 34A is respectively disposed on the +Z sides of the lens support 37 and the front side magnet support 36A, so that the inner side retaining part 34a of the front side spring component 34A is connected with the front side connecting end 37a of the lens support 37, and the outer side retaining part 36b of the front side spring component 34A is connected with the front side end part 36a of the front side magnet support 36A.
Then, as shown in FIG. 17C, the front side spring component mounting clamp 41A and the centering clamp 41C are dismounted from the assembled actuator unit 40.
At an embedding part between the centering clamp 41C for assembling the actuator unit 40 and the front side spring component mounting clamp 41A or the back side spring component mounting clamp 41B, loosening is easily occurred between the clamps for errors of machining dimension and the like, and loosening is also easily occurred between the clamp and the component for the dimensional deviation of each component such as the lens support 37.
Therefore, for example, under the condition that the gap between the inner wall 37d of the lens support 37 and the outer diameter of the centering clamp 41C is large, during the process of converting the working procedure of connecting the back side spring component 34B as shown in FIG. 17A to the working procedure of connecting the front side spring component 34A as shown in FIG. 17B, the lens support 37 connected with the inner side retaining part 34a may be inclined toward the direction (X-axis direction, Y-axis direction) orthogonal to the Z axis, or the back side magnet support 36B connected with the outer side retaining part 34b may be inclined toward the direction (X-axis direction, Y-axis direction) orthogonal to the Z axis, or the wrist parts 34c of the back side spring component 34B may be distorted in the direction orthogonal to the Z axis.
In the state that the wrist parts 34c of the back side spring component 34B are distorted, while the front side spring component 34A is respectively connected with the lens support 37 and the front side magnet support 36A, the wrist parts 34c of the back side spring component 34B in the actuator unit 40 still keep at a distorted state. Therefore, when the centering clamp 41C and the front side spring component mounting clamp 41A are dismounted to enable the lens support 37 to be at a freely suspended state, the stress generated by the wrist parts 34c of the back side spring component 34B is also transmitted to the wrist parts 34c of the front side spring component 34A.
As a result, as shown in FIG. 17C, the lens support 37 is twisted around the axis forming straight angle with the Z axis as shown in a rotating arrow R, until the stress integrally generated by the wrist parts 34c of the front side spring component 34A and the back side spring component 34B achieves a balanced angle.
As mentioned above, the base 39 is mounted at the back of the actuator unit 40 in the lens driving device, the back side magnet support 36B is fixed on the base 39, and the back side end part 37e of the lens support 37 abuts against the front end of the limiting part 39e of the base 39 and the lens support 37 is supported in the state of being subjected to the offset towards the front of the Z axis direction.
Therefore, as shown in FIG. 17D, when the back side end part 37e of the lens support 37 abuts against the limiting part 39e so as to be positioned at the backmost position, even if the lens support lens 37 is suspended distortedly on the actuator unit 40, the lens support 37 cannot be distorted, and will stay toward the Z axis direction.
However, when the coil 38 operates to enable the lens support 37 to move forwards in front of the Z axis and to enable the back side end part 37e to deviate from the limiting part 39e, the spring component 34 forms a twisted state as shown in FIG. 17C again, and the suspended lens support 37 is inclined.
When the actuator unit 40 is assembled in the lens driving device 30, the lens support 37 can be inclined during auto focus, and thus the lens 31 retained on the lens support 37 may be inclined. The image focused on the image sensor is twisted for the inclined lens 31, which leads to color permeation or dimming, and the problem of image quality degradation such as image stress.